The present invention relates to controlling a power amplification stage (also known as an output stage) of an audio signal amplifier.
Class A amplifiers are characterized by having a quiescent point in the linear operating region of their output devices. The quiescent point is also selected so that any input signal will not drive the output devices to saturation or cut-off. In this way, the output devices conduct through 360 degrees of an input signal.
Whilst this guarantees excellent linearity and minimal distortion—both highly desirable in audio applications—conventional Class A arrangements are configured to pass all of the current necessary to drive a load at full rated power, even at low signal levels. This means that their efficiency is typically very poor, and requires the incorporation of careful thermal management in the form of sufficiently large heatsinks, or the ability to move to a more efficient mode of operation such as Class AB to reduce the amount of current dumped by the output devices.